Superfund Innovative Technology Evaluation (SITE)
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This project evaluated an innovative approach for removing inorganic contaminants from the liquid phase at Superfund sites. In the process, called adsorptive filtration, metals are collected by attachment to a thin layer of ferrihydrite (iron oxide) that has been immobilized on the surface of sand grains. The modification of the surface of the sand allowed the grains to adsorb soluble heavy metals and to remove particulate metals by filtration as a solution passed through a column packed with the media
The metals studied were Cd, Cu, and Pb, present at concentrations of 0.5 or 5 mg/L each, in synthetic solutions. A few preliminary tests were also conducted to evaluate removal of the toxic oxyanions of As and Se. The effects on process performance of solution pH, the empty bed detention time, and the presence of complexing agents, oil, surfactant, and biodegradable substances were evaluated. In addition, the potential to regenerate the media after a run was investigated, including both the kinetics and overall efficiency of the regeneration process. Finally, a model waste solution from a Superfund site was treated by adsorptive filtration in a small-scale test.
In general, adsorptive filtration proved to be an efficient treatment process. Soluble and particulate forms of all the metals tested could be removed from the water stream at both concentrations tested. The contact time required for treatment was minimal (<5 min), and treatment was successful at moderate pH values (near 9). Removal efficiencies ranged from about 70-9996, depending on the treatment conditions. Regeneration was also fairly rapid and efficient, with metal concentrations in the regenerant solutions reaching several hundred times those of the influent. Over the duration of the tests, there was no indication that the media was deteriorating. Finally, the process was shown to be applicable for removing Zn from a waste stream generated at a Superfund site. Overall, the project adequately demonstrated the potential applicability of the process, and it appears that the process is appropriate for testing at a larger scale.